This Saturday and Sunday, people around the world will be biking naked as part of a celebration called the World Naked Bike Ride. This has been going on for a few years now as a way to celebrate both the human form in all its bare glory as well as promoting biking as a greener way to get around.
The ride in NYC takes place this Saturday starting at 5pm in East River Park, just south of the Williamsburg Bridge. The actual route is something of a secret so that the police cannot harrass them too much. The riders say that it's the one day you can ride naked through the streets. Technically this is not true but there is always safety in numbers, of course. Nudity is not required as the policy is "bare as you dare".
Here's a YouTube video of last year's ride to give a sense of the whole thing. Note that this is NSFW....as you might guess a video of World Naked Bike Ride Day would be :)